Determinants of myocardial water content during cardiopulmonary bypass

Increased myocardial water content has been shown to be accompanied by decreased ventricular compliance. We determined the effect of cardiopulmonary bypass for 2 (2CBP) and 3 (3CBP) hours, hypercalcemic cardiopulmonary bypass (CA), normothermic cross-clamping (CCNT), and hypothermic cross-clamping (CCHT) on myocardial water content. We found that myocardial water content was increased in the CA, CCNT, and CCHT groups. The distribution of myocardial water was different in the three groups with edema. Water accumulated in the subepicardium more than in the subendocardium in the CCNT group. The distribution of myocardial water and the histologic examinations suggest that subendocardial edema occurs in CA and CCHT because of venous obstruction in the subendocardium with intact capillary membranes. The greater accumulation of water in the subepicardium in CCNT may be related to increased capillary permeability and decreased interstitial pressure in the subepicardium. We conclude that myocardial edema during bypass may be greater in the small, firmly-contracted heart and after normothermic or hypothermic aortic cross-clamping.